dummy head?

[Maxx]

spot this in other web site and no idea what it is / it does

and advantage of having it?

can someone explain?

thanks heaps

[Sneaker]

Hard to see in the photo but is this a wild block extension? Kind of like the one for the RB26DETT you can get that takes it up to 3ltr? Very hard to make out how big it is though.

[Chris Wilson]

It takes the place of the head itself, and preloads the block with the stresses that bolting a REAL head down would do (supposedly, see later) and thus allows the boring of the block to be more accurate. The thinking is that torquing a head down imposes stresses in the block, making a round and parallel bore hole distorted once the head is bolted on. However, my own thinking is that heat stresses probably cause more bore distortion than that of the head bolt or stud torques, so maybe the block should be bored at operating temperature? It can all get very subjective and complex. Just how appropriate the torque loading from a solid block of steel clamped onto the top of the block is in comparison to a cast alloy head is almost anyones guess. All IMO.

[TODA AU]

Not all dummy heads are made of steel, some are alloy...

Also, some companies do bore & hone their engines @ specific controlled temperature.

Including these control measures all this adds to the acuracy & total cost of the job.